Achuthan & Stradner 1969. Calcareous nannoplankton from the Wemmelian stratotype. Bronnimann, P.; Renz, H. H.[Eds]. Proceedings of the First International Conference on Planktonic Microfossils. Geneva 1967., Proceedings of the First International Conference on Planktonic Microfossils. Geneva 1967. E. J. Brill, Leiden Vol.1.1967 [1969]., 1969: 1-13. Chapter pagination: 1-13